1. Field of the Invention
The present invention relates to an inductor and a DC-DC converter including the inductor.
2. Description of the Related Art
Nowadays, with miniaturization of an electronic device, a DC-DC converter used in the electronic device is also required to become smaller and reduce its profile. Because of this, an inductor of the DC-DC converter, the inductor needing a relatively large space, is required to become smaller and reduce its profile.
One example of such a small inductor is an inductor disclosed in Japanese Patent No. 3,410,876. The inductor includes a planar spiral coil, an insulating layer sandwiching the spiral coil from its opposite sides, and a magnetic layer sandwiching the insulating layer.
Another example is an inductor disclosed in Japanese Unexamined Patent Application Publication No. 1-157507. The inductor has a structure in which a spiral coil is disposed between neighboring layers of three insulating layers and a layer member made up of the spiral coils and the insulating layers is sandwiched between magnetic layers.
Unfortunately, for the inductors described in the above-mentioned patent documents, insulating layers are indispensable, and the insulating layers result in a limiting factor for a reduction in profile. With the inductors described in the above-mentioned patent documents, magnetic fields occurring in the plurality of spiral coils are combined, so if the magnetic layers are thin, magnetic saturation tends to occur and direct-current superimposition characteristics are poor. In particular, for an output inductor of a DC-DC converter, its load current may be large depending on the use; when the inductor tends to reach magnetic saturation, characteristics tends to degrade. Meanwhile, in order to make magnetic saturation less likely to occur and direct-current superimposition characteristics better, thick magnetic layers are necessary. This also results in a limiting factor for a reduction in profile.